Compression-tension transducer, especially for electromechanical braking systems

ABSTRACT

A pressure force sensor has two oppositely located connectors for a force introduction to an inside located force sensor module which emits an output signal as a function of an external pressure force, a fork arm attached to each of the connectors and having two fork ends which are offset by 90° and enclose the force sensor module, and pressure elements located between respective bases of the fork arms and a force introduction surface of the force sensor module, the pressure elements being also laterally enclosed by angled sections of the fork ends, so that pressure forces as well as tensile forces can be passed from the connectors to the force introduction surface of the force sensor module.

BACKGROUND OF THE INVENTION

The invention relates to a pressure force sensor, in particular for thedetection and control of wheel braking forces in connection withelectro-mechanical brake systems for motor vehicles.

In connection with a brake device for motor vehicles known from EP 0 566133 B1, the required braking force is transferred to the wheels by meansof a hydraulic servo unit. The cylinder pressure generated by pushingthe brake pedal down is measured in a main cylinder, and this measuredvalue is employed as a control signal for a hydraulic control device foroptimizing the braking effect.

It is necessary, in particular in connection with electro-mechanicalbraking systems, to detect suitable control values for optimizing thebraking effect individually at each wheel, which can then be supplied toan electronic control device. With brake systems controlling the wheelbrake force or respectively the wheel brake torque, it is useful todetect these wheel brake forces or respectively torque directly at thewheel, if possible.

SUMMARY OF THE INVENTION

The pressure sensor in accordance with the present invention has a forkarm attached to each connector and having two forked ends which areoffset by 90° and enclose the force sensor module, and pressure elementsare located between the bases of the fork arms and the forceintroduction surface of the force sensor module, which are laterallyalso enclosed by angled sections of the fork ends so that pressureforces as well as tensile forces can be passed from the connectors tothe force introduction surface of the force sensor module.

The pressure sensor in accordance with the invention can be employed forthe detection of all braking torques transmitted at the braked wheel andwhich makes a suitable signal available for further processing in abrake control device.

Magneto-elastic pressure sensors are used in an advantageous manner,which are customarily used for sensing pressure forces which, forexample, also suffices for controlling forces in the brake calipers ofthe brake system. In accordance with the invention, the requirement fortwo pressure sensors for making a torque control for forward and reversedriving possible is avoided in a simple manner. The problem of forceintroduction and the zero drift point in connection with overloads underchanging load conditions, such as can occur in connection with singlesensor concepts during forward and reverse travel, has been solved inaccordance with the invention.

A conversion of tensile and pressure forces, while keeping the pressureforce introduction, is therefore possible in a particularly advantageousmanner with the pressure sensor in accordance with the invention,because of which a use of the pressure force/pressure sensor fordetecting changing tensile and pressure forces can also be employed forgeneral force sensing purposes.

A control of the wheel brake torque can be performed in a simple mannerby detecting the support force in the mechanical brake device at atorque support which transmits tensile and pressure forces, wherein thewheel brake is hingedly seated and is supported by this torque support.A control of the braking torque in electronically controlled brakesystems with alternating load directions is possible with only onepressure force sensor for both directions by using the output signal ofthe pressure sensor.

Embodiments which are also advantageous are recited in the furtherdependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of a pressure sensor in accordance with theinvention will be explained by means of the drawings. Shown are in:

FIG. 1, a representation of the parts of the pressure sensor, and

FIG. 2, the assembled ready-to-function pressure sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Parts of a pressure sensor, which has a not completely assembled forkarm 1 (see the lateral view on top) and a fork arm 2 (see the top viewin the center), are represented in FIG. 1. A force sensor module 3 andrespective pressure elements 4 and 5 are furthermore represented. Thefork arm 1 has a fixedly mounted fork end 6 (see the top) and a fork end7, which can be attached at the end of assembly. Reference is made toFIG. 2, which shows the assembled pressure sensor 8, for explaining thefunctioning of the pressure sensor.

Oppositely located connectors 9 and 10 are located on the fork arms 1and 2, on which the tensile or pressure force to be detected acts. Apossible employment of the pressure sensor for detecting braking forcesat motor vehicle wheels can be taken from the prior art, EP 0 566 133 B1(FIG. 1), wherein a pressure sensor is housed in a hydraulic servo unit,and the pressure forces between the wheel brake and a torque support aredetected.

In accordance with FIG. 2, the cube-shaped magneto-elastic force sensormodule 3 is enclosed by the two fork arms 1 and 2, which arerespectively turned by 90° in relation to each other. The fork ends 6and 7, as well as the fork end 11 and the fork end, not visible, of thefork arm 2, here engage respectively one of the pressure elements 4 and5 by means of angled sections 12 in such a way that tensile forces arealso introduced as pressure forces via the pressure elements 4 and 5into the force sensor module 3.

Thus, with the exertion of pressure on the connectors 9 and 10, thepressure force is transferred directly at the bases of the fork arms 1and 2 via the pressure elements 4 and 5 to the force sensor module 3.With the connectors 1 and 2 put under a tensile load, the angledsections 12 of the fork ends transfer the force to the force sensormodule 3 and an output signal can be generated in the same way. As longas only tensile forces occur, the pressure elements 4 and 5 could alsobe fixedly connected with the fork arms 1 and 2.

In case of a change of the direction of pressure, all forces acting onthe force sensor module 3 must be detected. For this it is necessarythat these pressure elements 4 and 5 can be disengaged in the directionof pressure and that therefore the pressure elements 4 and 5 rest on theone side directly against the base of the fork arms 1 and 2 and on theother side on the force introduction surface of the force sensor module3.

For an improved assembly capability, the one fork arm 1 is divided inthe area of a contact zone with the force sensor module 3 and has, asdescribed above, a separate fork end 7, which is attached in such a waythat an assembly is made possible in spite of interfering contours, forexample for cable lead-throughs for the force sensor module 3, etc.

In an embodiment not represented here, the fork arm 1 for example canalso form a unit with the pressure element 4, wherein the requireddisengagement can be realized by a loose engagement of the fork arm 1 onthe connector 9.

In a reversal of the principle of force reversal it is furthermorepossible to embody the pressure elements 4 and 5 in a fork shape and inplace thereof to use appropriately simpler connectors 9 and 10.

The design of the force sensor module 3 can be in accordance withconventional techniques, for example as described with a magneto-elasticmodule, wherein minor changes of the mechanical shape by pressure actionlead to a change of the magnetic properties, and this change can beelectronically evaluated. A design with wire strain gauges, whichexperience a change in electrical resistance when mechanically stressed,can be employed here without departing from the principle of theinvention. Other elements suitable for detecting pressure force, whichundergo a change of their electrical properties under mechanicalstresses, can also be employed here.

What is claimed is:
 1. A pressure force sensor, comprising twooppositely located connectors for a force introduction to an insidelocated force sensor module which emits an output signal as a functionof an external pressure force; a fork arm attached to each of saidconnectors and having two fork ends which are offset by 90° and enclosethe force sensor module; and pressure elements located betweenrespective bases of said fork arms and a force introduction surface ofthe force sensor module, said pressure elements being also laterallyenclosed by angled sections of said fork ends, so that pressure forcesas well as tensile forces can be passed from said connectors to theforce introduction surface of the force sensor module.
 2. A pressureforce sensor as defined in claim 1, wherein said at least one of saidfork arms is composed of two pieces, one of said fork ends of arespective one of said fork arms being attachable to said fork arm afterthe pressure force sensor has been assembled.
 3. A pressure force sensoras defined in claim 2, wherein a removable fork end is composed of onepiece with one of said pressure elements, one of said connectorsassociated with this fork arm being loosely held on this fork arm.
 4. Apressure force sensor as defined in claim 1, wherein said fork arms areformed of one piece with said pressure elements, said connectorsassociated with said fork arms being loosely held on a respective one ofsaid fork arms.
 5. A pressure force sensor as defined in claim 1,wherein the force sensor module is a magneto-electric force sensor.